Polarization modulation with amplitude differential

ABSTRACT

Wireless data communication method and apparatus using two electromagnetic signals having different polarizations. Codes related to relative values of the amplitudes of the two signals are generated in correspondence with data to be transmitted. The signals are modulated according to the codes using phase shift keying and amplitude shift keying. The amplitude shift keying modulates the two electromagnetic signals by changing the difference between their two amplitudes in accordance with data encodings. The two signals are transmitted to receiver, which decodes the phases and relative amplitudes to obtain the codes, and reproduces the data from the obtained codes.

FIELD OF THE INVENTION

The present invention relates to a method, apparatus, and system fortransmitting information by modulating a carrier wave or receivinginformation in a modulated carrier wave in wireless communication.

BACKGROUND

Various schemes for communicating information by modulating a carrierexist. Typical examples of such schemes are frequency shift keying(FSK), phase shift keying (PSK), and amplitude shift keying (ASK).

In phase shift keying, phases (0, pi) of a carrier are transmitted incorrespondence with input data (0 or 1). Given two phases, one data bitmay be transmitted per phase shift. With other phase shift keyingschemes, more than one bit per shift may be transmitted. For example, inquadrature phase shift keying (QPSK), two bits successively input areregarded as one symbol, and phases (pi/4, 3pi/4, 5pi/4, 7pi/4) of acorresponding carrier are transmitted.

A quadrature phase shift keying hierarchy in which important data andunimportant data are differentiated from each other is disclosed inPublished Unexamined Japanese Patent Application No. 5-276211.

In amplitude shift keying, the amplitude A of a carrier is modulated tocarry, for example, two values (A/2, A) in correspondence with inputdata (0 or 1). The carrier modulated by amplitude shift keying isreceived by a receiver. The amplitude level of the received carrier isdetected, and the input data corresponding to the detected amplitudelevel is reproduced. In this simple example, 1 is obtained as the inputdata when the amplitude level of the received wave is A, and 0 isobtained when the amplitude level is A/2. In this kind of amplitudeshift keying, the rate of data transmission may be increased byincreasing the number of different amplitude levels, i.e., increasingthe number by which the amplitude A is divided.

Amplitude shift keying in wireless communication, however, can be easilyaffected by propagation path disturbances such as disturbances due toweather conditions such as rain or clouds. Fading may occur such thatthe received wave amplitude fluctuates in a short cycle. The amplitudeof the carrier consequently fluctuates unpredictably, and the bit errorrate thereby increases. In the above-described example, if a carrierwith amplitude A, which for example corresponds to input data 1,undergoes a disturbance that results in the amplitude being halved toA/2, incorrect input data 0 is reproduced. For this reason, phase shiftkeying, which is advantageous in terms of noise resistance, isfrequently used instead of amplitude shift keying.

On the other hand, cable broadcasting such as CATV is free from theabove-described attenuation problem, and amplitude shift keying iseffective in this environment. For cable broadcasting, therefore, keyingschemes that combine amplitude shift keying and phase shift keying arebeing used. Such a keying scheme has been introduced, for example, inPublished Unexamined Japanese Patent Application No. 63-175542.

For example, binary phase shift keying and binary amplitude shift keyingmay be performed on each of two polarized carrier waves, in this casehorizontally and vertically polarized waves that are orthogonal to eachother. In this case, the phase shift keying and amplitude shift keyingtogether enable transmission of 2×2=4 bits of data per polarization.Accordingly, 4×4=16 bits of data per baud can be transmitted on theentire carrier. Since phase shift keying is combined with amplitudeshift keying, the amplitude of each polarized wave is determined by theamplitude of the envelope of the polarized wave.

As described above, if amplitude shift keying and phase shift keying areperformed in combination on each of two independently polarized waves, amultiplicity of information bits can be transmitted in one frequencyband. However, this keying scheme is not effective in wirelesscommunication, because the above-described attenuation of carrieramplitude by propagation-path disturbances cannot be avoided. That is,the influence of a disturbance may fluctuate with time, thereby causingthe absolute value of the amplitude of the received carrier also tofluctuate with time, resulting in failure to reliably reproducetransmitted data.

Therefore, an object of the present invention is to provide a wirelesscommunication method which extends digital transmission capabilities sothat amplitude shift keying may be applied to two differently polarizedwaves without suffering the problem of excessive error rates caused bypropagation-path disturbances acting on carrier signal amplitudes.

SUMMARY

A communication method in accordance with the present invention mayinclude a step of generating, in correspondence with data to betransmitted, codes related to relative values of the amplitudeintensities of a first polarized wave and a second polarized waveindependent of the first polarized wave, a step of transmitting thefirst and second polarized waves by modulating the first and secondpolarized waves according to the codes, a step of receiving thetransmitted first and second polarized waves and detecting the amplitudeintensities of the first and second polarized waves, a step of obtainingthe codes by decoding from the detected amplitude intensities, and astep of reproducing the transmitted data from the obtained codes.

A high degree of independence can be maintained between the first andsecond polarized waves even during wireless transmission. Consequently,data carried by modulation is also independent between the two polarizedwaves, and the first and second polarized waves are therefore capable ofsustaining high data throughput in a single frequency band.

The relative values of the amplitude intensities of the first and secondpolarized waves are not substantially affected by attenuation due topropagation path disturbances. Therefore, the transmitted data can bereproduced with improved accuracy by demodulation by using the codesrelated to the relative values.

A communication apparatus in accordance with the present invention mayinclude a transmitter which transmits a first and a second polarizedwave independent of the first polarized wave, a code data assigner whichassigns codes corresponding to the data to be transmitted and related tothe relative values of the amplitude intensities of the first and secondpolarized waves to be transmitted, and a modulator which modulates thefirst and second polarized waves to the amplitudes corresponding to thecodes assigned by the code data assigner.

Another communication apparatus in accordance with the present inventionmay include a receiver which receives a first polarized wave and asecond polarized wave, a relative amplitude detector which detectsrelative values of the amplitude intensities of the first and secondpolarized waves received by the first and second receivers, a decodingsection which decodes to obtain the codes from the relative valuesdetected by the relative amplitude detector, and a reproduction sectionwhich reproduces the transmitted data from the codes decoded by thedecoding section.

The above-described communication method may be carried out by usingthis communication apparatus. Also, a wireless communication system maybe constructed by using a plurality of the above-described communicationapparatus.

In the description that follows, the first polarized wave may bereferred to as the “horizontally polarized wave” and the secondpolarized wave may be referred to as the “vertically polarized wave.”

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in further detail with reference tothe attached drawings, wherein:

FIG. 1 is a block diagram outlining amplitude shift keying in acommunication method of the present invention;

FIG. 2 shows a relative-coordinates coding matrix obtained in anamplitude shift keying scheme in an embodiment of the present invention;

FIG. 3 is a block diagram showing a method of transmission in atransmitter used in the communication method of the present invention;

FIG. 4A is a block diagram showing the method of receiving in a receiverused in a communication method of the present invention;

FIG. 4B is a block diagram showing a method of data processing in arelative amplitude detector 22 shown in FIG. 4A; and

FIG. 5 shows a coding matrix for amplitude values obtained in anamplitude shift keying scheme in an embodiment of the present invention.

DETAILED DESCRIPTION

A transmitter suitable for use in the communication method of thepresent invention will first be described with reference to the blockdiagram of FIG. 3. A transmitter 50 includes a data distributor 52 whichdistributes digital data to be transmitted, phase and amplitude shiftkeying modulators 54 a, 54 b, 58 a, and 58 b which perform phase shiftkeying and amplitude shift keying on distributed polarized waves,up-converters 56 a and 56 b which perform processing includingamplification on the polarized waves on which phase shift keying hasbeen performed, adders 60 a and 60 b each of which adds together thepolarized waves on which phase shift keying and amplitude shift keyinghave been performed, and horizontally and vertically polarizedtransmitting antennas 64 a and 64 b which transmit the polarized wavesadded together and power amplified.

The data distributor 52 may be included in the above-described code dataassigner, and the horizontally and vertically polarized transmittingantennas 64 a and 64 b may be combined so as to have a common physicalstructure.

Horizontally and vertically polarized waves transmitted from thetransmitter 50 are received by a receiver 10 shown in the block diagramof FIG. 4A. The receiver 10 may include a parabolic antenna 12 whichreceives the polarized waves, horizontal and vertical high-frequencyconversion circuits 14 a and 14 b which respectively detect thehorizontally and vertically polarized waves, signal intensity detectors18 a and 18 b which detect the amplitude intensities of the polarizedwaves detected and received through down-converters 16 a and 16 b, QPSKdemodulators 24 a and 24 b which perform quadrature phase shift keyingdemodulation of the received polarized waves, a relative amplitudedetector 22 which performs amplitude shift keying demodulation of thepolarized waves received from the signal intensity detectors 18 a and 18b, and a digital data processor 26 which combines data obtained from thedemodulated polarized waves to reproduce transmitted data.

Any suitable method may be used to separate the signals carried on thehorizontally and vertically polarized waves from the parabolic antenna12 and supply the signals to the high-frequency conversion circuit 14.Although the horizontally and vertically polarized waves may beattenuated by propagation path disturbances, the independence of the twopolarized waves and the difference between the amounts of attenuation inthe polarized wave planes are normally maintained.

Electric waves collected by the parabolic reflecting plate 12A of theantenna 12 are guided to a horn portion of a low-noise block converter(LNB). At the end of the horn portion, the horizontally and verticallypolarized waves are separated by the two high-frequency conversioncircuits 14 a and 14 b, and are supplied to the down-converters 16 a and16 b by the LNB circuit.

Alternatively, separate parabolic antennas specially provided for thehorizontally and vertically polarized waves may themselves separate thehorizontally and vertically polarized waves. Any other method forseparating the horizontally and vertically polarized waves may be used,and the antenna is not limited to any particular type.

It is assumed here for descriptive convenience that amplitude shiftkeying used in this embodiment is performed in the transmitter 50 sothat each polarized wave has five values, and that each polarized wavecan be expressed by an integer value (5, 6, 7, 8, and 9) after beingamplified. These amplitude values correspond, respectively, to data tobe transmitted (000, 001, 010, 011, 100). A coding matrix 500 such asshown in FIG. 5 is obtained by plotting the amplified amplitude (5, 6,7, 8 and 9) of the horizontally polarized wave along the abscissa andthe amplified amplitude of the vertically polarized wave along theordinate. By the coding matrix, data of 5×5=25 values to be transmittedare coded as shown in FIG. 5 by means of the set of amplified amplitudeintensities of the polarized waves.

Conventional phase shift keying may be used to modulate each polarizedwave. If each polarized wave has, for example, four values as a resultof phase shift keying performed in addition to the above-describedamplitude shift keying, 4×4×5×5=400 data points can be coded withrespect to a particular frequency band.

The method of amplitude shift keying demodulation of the horizontallyand vertically polarized waves in the relative amplitude detector 22 inthis embodiment will now be described in detail.

The block diagram of FIG. 4B shows the relative amplitude detector 22 inthis embodiment. The relative amplitude detector 22 may includeanalog-to-digital converters 32 a and 32 b which convert amplitudeanalog data in the polarized waves sent from the signal intensitydetectors 18 a and 18 b, an amplitude difference detector 36 whichdetects an amplitude difference D from the digital data on theamplitudes of the polarized waves, and dividers 38 a and 38 b whichobtain relative values of the amplitude intensities of the polarizedwaves from the digital data on the amplitudes of the polarized waves andthe amplitude intensity difference D detected by the amplitudedifference detector 36.

The relative amplitude detector 22 may also include a data comparator 40which compares the amplitude intensity relative values received from thedividers 38 a and 38 b with a code search table 30 to detect the mostproximate points, and an amplitude data decoder 42 which receives dataat the most proximate point and/or the amplitude intensity differenceD=0 signal generated from the amplitude difference detector 36, andgenerates final data.

The data comparator 40 or the amplitude data decoder 42 may be includedin the above-described decoding section or reproduction section.

The amplitude difference detector 36 subtracts the amplitude intensityof the vertically polarized wave from the amplitude intensity of thehorizontally polarized wave, and detects the absolute value of thedifference between the amplitude intensities of the two polarized waves.This amplitude intensity difference D has different positive valuesdepending on the modulating signal applied to the amplitude, and is zerowhen the amplitudes of the two polarized waves are equal. When theamplitude intensity difference D is not zero, the ratio of the absolutevalues of the amplitudes of the two polarized waves and the amplitudeintensity difference D are obtained to generate the relative values ofthe two amplitude intensities.

The amplitude intensity difference D and the amplitude intensityrelative values will now be described further. When D is zero, thesignal detected by the amplitude difference detector 36 is sent directlyto the amplitude data decoder 42 in the relative amplitude detector 22.Otherwise (i.e., D is not zero), the amplitude intensity difference Ddetected by the amplitude difference detector 36 is sent to the dividers38 a and 38 b for computation of relative value coordinates (horizontalamplitude intensity/D, vertical amplitude intensity/D). The relativevalue coordinates computed from the amplitude of the received carrier bythe dividers 38 a and 38 b will be referred to as “received relativevalue coordinates.” The relative value coordinates are differentiatedfrom relative value coordinates coded in the code search table 30described below.

Because the quantity obtained by dividing the amplitude intensity by theamplitude intensity difference D remains constant even when theamplitude intensity changes, the influence of amplitude attenuation onthe received relative coordinate values due to propagation pathdisturbances can be avoided.

FIG. 2 shows the code search table 30. The relative value coordinatesare different from each other except for those on a diagonal line, andare coded as shown in FIG. 2. The coordinates on the diagonal lines arenot discriminated from each other. These are given a code X, because Dis zero. In this embodiment, the amplitude intensity after amplitudeshift keying is an integer in the range 5 to 9. Consequently, therelative amplitude detector 22 is capable of coding into A to T and X,and thus supports the twenty-one encodings shown in FIG. 2.

The code search table 30 may be stored in advance in a storage deviceprovided outside or inside the relative amplitude detector 22, forreference at the time of demodulation.

Data on the above-described received relative value coordinates computedby the dividers 38 a and 38 b is sent to the data comparator 40 to becoded. The data comparator 40 first compares the received relative valuecoordinates with coded relative value coordinate data in the code searchtable 30. Since the amplitude signal of the carrier may be changed bypropagation path disturbances in wireless communication as describedabove, the data comparator 40 detects the relative value coordinate dataclosest to the received relative value coordinates from the code searchtable 30. The relative value coordinate data to be detected is relativevalue coordinate data coded into the twenty items A to T shown in FIG.2.

The closest relative value coordinate data thus detected is sent to theamplitude data decoder 42. The amplitude data decoder 42 extracts thecorresponding codes from A to T in the code search table 30. When theamplitude intensity difference D=0 signal comes from the amplitudedifference detector 36, the amplitude data decoder 42 determines thatthe amplitude intensity difference is zero, and gives code X. Theextracted amplitude shift keying codes are sent to the digital dataprocessor 26 and combined with codes obtained by QPSK demodulation, thusdecoding to obtain the transmitted data.

FIG. 1 is a block diagram showing an amplitude shift keyer 100 that issuitable for use in the communication method of the present invention.The exemplary amplitude shift keyer 100 includes blocks for detectingthe amplitude intensity difference 101, dividing the amplitude of thehorizontally polarized signal by the detected difference 102, dividingthe amplitude of the vertically polarized signal by the detecteddifference 103, performing code search 104 and code detection 105, anddetermining the appropriate digital value 106. The communication methodof the present invention is not, however, so limited. For example, moreor less than five amplitude levels may be used, as well as five. Also,the invention is not limited to the use of the exemplary phase-shiftkeying modulation scheme that is discussed here in combination withamplitude shift keying. The scope of the communication method of thepresent invention includes as well any other amplitude shift keyingmodulation and demodulation methods for standardizing and coding theamplitude intensity by using the amplitude intensity difference D.

The communication apparatus of the present invention is not limited tothe configuration of the above-described embodiment. The componentscorresponding to the relative amplitude detector that detects relativevalues of the amplitude intensity, the decoding section that decodes toobtain codes corresponding to the relative values by referring to thecode search table, and the reproduction section that reproducestransmitted data from the codes may be included in any forms in thecommunication apparatus of the present invention.

Also, any suitable method may be used to separate the horizontally andvertically polarized waves, and the transmitting and receiving antennais not limited to any particular type. It is not a requirement of theinvention that the two polarized waves be orthogonal to each other.Further, the two polarized waves may be circularly polarized waves suchas right-hand and left-hand circularly polarized waves. Any twopolarized waves may suffice if they can carry data independently of eachother.

Wireless communication in the context of the present invention may bepreferably performed by setting sharp directivity at high frequencies.However, the communication method of the present invention is notlimited to wireless communication in a particular frequency band.

According to the communication method of the present invention, twopolarized waves that are independent of each other are used. Amplitudeshift keying and phase shift keying may be performed on each polarizedwave, thereby enabling high data throughput in wireless communication.

In particular, since the quantity obtained by dividing the amplitudeintensity of each of the two polarized waves by the amplitude intensitydifference D is constant even when the amplitude intensity changes, theinfluence of amplitude attenuation due to propagation path disturbanceson the received relative value coordinates can be avoided. That is,since modulation and demodulation are performed by using the relativevalues of the amplitude intensities in the communication method of thepresent invention, the communication method of the present invention iscapable of avoiding the influence of propagation path disturbances, incontrast to the conventional modulation scheme using the absolute valueof the amplitude intensity.

Thus, the communication method of the present invention ensures wirelesscommunication with improved stability against propagation pathdisturbances, and thereby enables high data throughput with accuracy.

1. A communication method, comprising the steps of: generating, incorrespondence with data to be transmitted, codes based on relativevalues of amplitude intensities of a first wave with a firstpolarization and a second wave with a second polarization, wherein thefirst and second polarizations are different; modulating the first andsecond polarized waves according to the codes; transmitting the firstand second polarized waves; receiving the transmitted first and secondpolarized waves; detecting relative amplitude intensities of the firstand second polarized waves; decoding the detected relative amplitudeintensities to obtain the codes; and reproducing the transmitted datafrom the obtained codes.
 2. The communication method according to claim1, wherein the codes are determined based on relative values which areratios of the amplitude intensities of the first and second polarizedwaves to a difference between the amplitude intensities of the first andsecond polarized waves.
 3. The communication method according to claim2, wherein said modulating step includes a step of performing phaseshift keying on the first and second polarized waves before transmittingthe first and second polarized waves.
 4. The communication methodaccording, to claim 2, wherein the first polarized wave and the secondpolarized wave are orthogonal.
 5. Communication apparatus, comprising: atransmitter which transmits a first wave having a first polarization anda second wave having a second polarization wherein the firstpolarization and the second polarization are different; a code dataassigner which assigns codes corresponding to data to be transmitted,based on relative values of amplitude intensifies of the first andsecond polarized waves; and a modulator which modulates the first andsecond polarized waves according to amplitudes corresponding to thecodes assigned by said code data assigner.
 6. Communication apparatuscomprising: a receiver which receives a first polarized wave and asecond polarized wave, where the polarization of the first wave differsfrom the polarization of the second wave; a relative amplitude detectorwhich detects relative values of amplitude intensities of the first andsecond polarized waves received by said receiver; a decoding sectionwhich decodes to obtain codes from the relative values detected by saidrelative amplitude detector; and a reproduction section which reproducestransmitted data from the codes obtained by decoding performed by saiddecoding section.
 7. A communication system for communicating data fromsource apparatus to destination apparatus, wherein the source apparatuscomprises a transmitter which transmits a first wave having a firstpolarization and a second wave a second polarization, wherein the firstpolarization and the second polarization are different, a code dataassigner which assigns codes corresponding to data to be transmitted andrelated to relative values of amplitudes intensities of the first andsecond polarized waves; and a modulator which modulates the first andsecond polarized waves according to amplitudes corresponding to thecodes assigned by said code data assigner, and further wherein thedestination apparatus composes a receiver which receives a firstpolarized wave and a second polarized wave, where the polarization ofthe first wave differs from the polarization of the second wave; arelative amplitude detector which detects relative values of amplitudeintensities of the first and second polarized waves received by saidreceiver, a decoding section which decodes to obtain codes from therelative values detected by said relative amplitude detector; and areproduction section which reproduces transmitted data from the codesobtained by decoding performed by said decoding section.